JP3758062B2 - Active filter control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active filter that compensates for a harmonic current flowing into a power supply system from a load device and reduces current distortion of the power supply system.
[0002]
[Prior art]
FIG. 3 is a main circuit diagram of a system line including an active filter. As shown in FIG. 3, the active filter 41 is provided between the system power supply 1 and the load device 3 generating the harmonic current, and compensates so that the harmonic current included in the load current does not flow into the power supply system. Outputs current. Reference numeral 2 denotes a power source impedance.
The active filter 41 includes a three-phase PWM converter 6 composed of high-speed switching elements, a DC capacitor 7 provided on the DC side of the three-phase PWM converter 6, and an AC reactor 5 provided on the AC side of the three-phase PWM converter 6. The compensation current is calculated based on the load current detected by the high-frequency filter 91 provided in parallel with the power supply on the power supply side from the AC reactor 5 and the load current detection current transformer 11, and the switching element of the three-phase PWM converter 6 is calculated. And a control device 81 that outputs a switching command.
[0003]
A method of calculating and outputting a compensation current command for canceling the harmonic current of the load current from the load current detected by the current transformer 11 using a three-phase two-phase conversion method is well known and will not be described. The compensation current command calculated and output by the device 81 is compared with the compensation current detected by the compensation current detection current transformer 10, the switching element of the three-phase PWM converter 6 is turned on and off, and the current of the active filter 41 is The instantaneous value is controlled.
[0004]
[Problems to be solved by the invention]
As described with reference to FIG. 3, high-frequency ripple current is generated by high-speed switching of the switching elements constituting the three-phase PWM converter in the active filter, and a high-frequency filter 91 including a capacitor and a resistor is provided to absorb the high-frequency ripple current. I have been.
However, the constant selection of such a high-frequency filter is greatly influenced by the power supply impedance. Increasing the filter resistance value increases the loss, and if it is too small, the resonance phenomenon that occurs between the fill capacitor and the power supply impedance can be suppressed. In addition, the power supply voltage is greatly fluctuated and not only an excessive current flows through the ripple absorption filter, but there is also a problem that it adversely affects other devices connected to the system.
The present invention was devised in view of the above points, and the object of the present invention is to solve these drawbacks and to provide a high-frequency filter 91 that absorbs high-frequency ripple current by the three-phase PWM converter 6 of FIG. In such an active filter 41, a control method for suppressing a resonance phenomenon between the filter capacitor in the high frequency filter 91 and another reactor (power supply impedance 2) is provided, and a control method for an active filter that does not require a damping resistor is provided. It is in.
[0005]
[Means for Solving the Problems]
That is, the means for achieving the object is configured as follows. An active filter control device comprising an active filter provided in a system line between a system power supply and a load device, and a load current detecting current transformer for detecting a load current and supplying the output to the active filter. The active filter includes a three-phase PWM converter having a direct current capacitor provided on the direct current side and an alternating current reactor provided on each phase on the alternating current side, and a harmonic filter capacitor provided in parallel with the alternating current reactor and the power source. A transformer for detecting the voltage of the harmonic filter, a compensation current detecting current transformer for detecting a three-phase PWM converter current, and a control device for controlling the three-phase PWM converter, the control device comprising: The outputs of the load current detection current transformer, the compensation current detection current transformer, and the transformer are input, and the harmonic current obtained by the transformer is input. Harmonic content of the filter capacitor voltage with a voltage harmonic component, the gain K times value of opposite sign of the voltage harmonic component and harmonic current, resulting in a high-harmonic current the load current detecting current transformer The compensation current is calculated by adding the obtained currents, and the switching of the three-phase PWM converter is controlled so that the output current of the three-phase PWM converter follows the compensation current.
[0006]
The effect is the same as that obtained when a damping resistor is connected in parallel to the high-frequency filter 9 of the active filter, and the resonance phenomenon between the power supply impedance 2 and the impedance of the high-frequency filter 9 is suppressed. The power supply current harmonics can be reduced.
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an example of a main circuit of an active filter according to the present invention. 4 is an active filter, 8 is a control device to which an output of a transformer 12 for voltage detection of a ripple absorption filter capacitor 9 is inputted. is there. In the figure, the same reference numerals as those in FIG. 3 denote parts having the same configuration and function.
In FIG. 1, the active filter 4 according to one embodiment enhances a high-frequency filter effect that absorbs a ripple current generated by switching of the switching element of the three-phase PWM converter 6 as compared with the conventional active filter 4, and Naturally, the resonance phenomenon generated by the filter capacitor 9 and the power source impedance is also suppressed, and its function is as follows.
[0008]
The load current detected by the current transformer 11 and the voltage of the high-frequency filter capacitor 9 detected by the transformer 12 are added by the control device 8, and a compensation current command calculation circuit using three-phase two-phase conversion is conventionally used. A compensation current command value Ic * obtained by adding a gain K-fold value of the reverse sign of the harmonic of the voltage of the high-frequency filter capacitor 9 to the current command is calculated and output.
Here, the basic technical idea of the compensation current method will be described with reference to FIG.
FIG. 2 is a system block diagram in which an active filter is provided. Vs is a system voltage, Zs is a system impedance, Is is a current flowing through the system impedance, and Ilc is a load device that generates a load current Il including a harmonic current. What is expressed as a current source, Icc is a compensation current source for generating a compensation current Ic by the three-phase PWM converter 6, and Zf is an impedance of the high-frequency filter 9.
In FIG. 2, the power supply current Is can be expressed as in equation (1).
Is = Zf (Il + Ic) / (Zs + Zf) + Vs / (Zs + Zf) (1)
[0009]
Since Zs is represented by sLs and Zf is 1 / sCf, equation (1) can be expressed as equation (2).
Is = {(I 1 + Ic) / (s · sLs × Cf + 1)} + sCf × Vs / (s · sLs × Cf + 1) (2)
Equation (2) indicates that the power source current oscillates and expands when (Il + Ic) is not zero because there is no damping element in the denominator.
Therefore, when the voltage Vf of the high frequency filter capacitor 9 is detected, the sign of the harmonic component Vfh is inverted, the gain K is multiplied, and the PWM converter 6 is controlled in addition to the conventional compensation current command Ic *, the compensation current Ic Can be expressed by equation (3).
[0010]
Ic = −Gn (s) × (−KVf + I1) (3)
Here, Gn (s) is a notch filter for the fundamental wave. Therefore, equation (1) can be expressed as equation (4).
Is = Zf [I1-Gn (s) × (−KVf + I1)] / (Zs + Zf)
+ Vs / (Zs + Zf) (4)
Since Vf is the voltage of the harmonic filter capacitor 9, it can be expressed by equation (5).
Vf = Vs−Zs × Is (5)
[0011]
From the above conditions, focusing only on the harmonics in the equation (4), the fundamental wave is removed by the notch filter, and the harmonic current Ish flowing out to the power source can be expressed by the equation (6).
Ish = ΔIl h / (1 + K × Zs + Zs / Zf) + (K + 1 / Zf) × Vsh / (1 + K × Zs + Zs / Zf) (6)
In the equation (6), ΔI l h is a harmonic current included in the load current, which is not compensated by the active filter, and Vsh indicates the harmonic voltage in the power supply voltage.
On the other hand, Zs is represented by sLs, and Zf can be represented by 1 / sCf. Substituting this into equation (6) yields equation (7).
Ish = ΔIl h / (1 + K × sLs + s · sLs × Cf)
+ (K + sCf) × Vsh / (1 + K × sLs + s · sLs × Cf) (7)
A damping element K × sLs exists in the denominator of the equation (7).
Therefore, the resonance phenomenon between the power source impedance and the harmonic filter capacitor can be suppressed by the harmonic current flowing out to the power source.
[0012]
【The invention's effect】
As described above, according to the present invention, by detecting the voltage of the ripple absorbing high frequency filter capacitor of the active filter and adding the harmonic component to the compensation current command value, the harmonic filter of the power system impedance and the active filter is obtained. Resonance phenomenon with the capacitor can be suppressed, and the resistance for damping can be reduced, thereby obtaining the advantage that the ripple current of the active filter can be absorbed better and the efficiency of the active filter device can be improved at the same time. .
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an active filter main circuit according to the present invention.
FIG. 2 is an explanatory diagram of a system line provided with an active filter.
FIG. 3 is a block diagram showing an example of a conventional active filter main circuit.
[Explanation of symbols]
1 System power supply 2 Power supply impedance 3 Load device 41, 4 Active filter 5 AC reactor 6 Three-phase PWM converter 7 DC capacitor 81, 8 Controller 91, 9 High frequency filter 10 Current detector 11 Current transformer 12 Transformer Ic Compensation current Icc Compensation current source Il that generates compensation current Load current Il c Load current source Is that generates load current System current Vs System voltage Zs System impedance Ls System inductance Zf Impedance of high-frequency filter Cf Capacity of high-frequency filter capacitor

Claims (1)

An active filter control device comprising an active filter provided in a system line between a system power supply and a load device, and a load current detecting current transformer for detecting a load current and supplying the output to the active filter. The active filter includes a DC capacitor provided on the DC side and a three-phase PWM converter having an AC reactor provided on each phase on the AC side, a high-frequency filter capacitor provided in parallel with the AC reactor and a power source, The transformer comprises a transformer for detecting the voltage of the high-frequency filter, a compensation current detection current transformer for detecting a three-phase PWM converter current, and a control device for controlling the three-phase PWM converter. The outputs of the detection current transformer, the compensation current detection current transformer, and the transformer are input, and the harmonic current obtained by the current transformer is input. Harmonic content of the filter capacitor voltage with a voltage harmonic component, the gain K times value of opposite sign of the voltage harmonic component and harmonic current, resulting in a high-harmonic current the load current detecting current transformer A control method for an active filter, comprising: calculating a compensation current by adding the generated currents; and controlling switching of the three-phase PWM converter so that an output current of the three-phase PWM converter follows the compensation current

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